I've been compiling a list of the various card strings and image links. If you find the string, you can easily find any other picture of the card.
For example, take [Cloned Eliminator] X-23+ whos Large card can be found here . If you look at the address, you can see the specific string that identifies this card. In this case, ca775557e3863221b37a025ddb0da1d9. You can take that and plug it into other addresses (or just change /l/ to /xs/, /s/ or /w/) to see other used variations for that card.
Unfortunately it doesn't help find unknown cards (or even identify known cards), but it does make finding and pulling specific known images quite easy.
Here is a link to my current database of card strings. It's still a WIP. If you know any stings that I don't have listed, please leave a comment letting me know.
Edit: Found two more image locations: m and xm. m is a medium sized image, xm is a closer medium image.